Developmental defects in cranial neural crest (CNC) result in numerous human congenital anomalies. The role of the Hippo-signaling pathway, an evolutionarily conserved organ size control pathway, in neural crest development is poorly understood. To investigate Hippo signaling in CNC derivatives such as calvarial bones, we specifically inactivated the Hippo component Salv, and Hippo downstream effectors Yap and Taz in CNC using the Wnt1cre driver and Wnt1cre2SOR drivers. Salv conditional knock-out (CKO) mutants had dramatically enlarged calvarial bones and cranial sutures with increased calvarial bone density, whereas Taz homozygous mutants that were also Yap heterozygous (Taz hom;Yap het CKO) mutants had a range of survival times from E14.5 to postnatal 8 weeks with a range of calvarial bone defects with Wormian bones and decreased calvarial bone density. In this proposed R03 study, we hypothesize that Yap/Taz-mediated signaling crosstalk in neural crest is required for normal cranial bone development and will study two aims: 1) To investigate the hypothesis that Yap/Taz mediate regulation by Hippo kinases and matrix stiffness during cranial bone development. 2) To investigate the hypothesis that Yap/Taz regulate genes important for proliferation and differentiation during cranial bone development. My research will focus on bone regeneration and treatment of severely injured bone. This R03 study will provide preliminary data and potential targets in bone regenerative medicine for my subsequent R01 application, which I hypothesize that Hippo signaling impedes while Yap promotes bone regeneration and recovery after injury.